Cancer is currently the second leading cause of death in the U.S. (only next to heart disease). A new promising area of advances in cancer treatment is the application of excess heat to cancerous tissue called “hyperthermia” therapy. In particular, nanoparticle-mediated hyperthermia offers hope for treating cancer with no side effects by selective thermal ablation of the cancer cells. For this purpose, several nanoparticle materials have been proposed that can transduce near infrared light or magnetic energy into heat. However, these approaches have limitations that make them unsuitable for real clinical usage.
Nanoparticle-enhanced imaging and thermal destruction of tumors has been demonstrated using near infrared light to illuminate and heat gold nanoshells and gold nanorods. Although this method shows promise for treating cancer, it is only effective for treating sub-surface cancers (less than a few mm deep) because of the scattering and attenuation of near infrared light by biological tissues.
Magnetic nanoparticles have long been proposed as agents for non-invasive imaging and inductive hyperthermal destruction of cancer. If magnetic particles can be targeted to cancer tissue, they serve as effective contrast agents for MRI detection of a tumor. This is due to the fact that magnetic nanoparticles enhance the T2 spin relaxation of water protons while leaving the T1 relaxation largely undisturbed and this difference can be used to greatly enhance MRI contrast. Magnetic field-based hyperthermia is also a potentially effective method for treating deep tissue cancer, but it suffers from the limited heating potential of the magnetic particles that are currently available. The highest reported thermal power dissipation factor using iron oxide particles is a relatively low ˜0.5 kW/g of particles. A further problem is that many magnetic particles lack long term magnetic stability and tend to aggregate in high electrolyte aqueous environments.
Recently, it has been discovered that Au nanoparticles can be heated remotely using a capacitively coupled radiofrequency (RF) field. If these particles can be targeted to a tumor, this RF heating can serve as an effective method for thermal destruction of deep tissue cancers. Curley and coworkers have heated Au nanoparticles using an RF field of 13.56 MHz, with diameters <50 nm at low ppm concentrations in water (Moran, et al, Nano Research, 2009, 2(5), 400-405). They report a high thermal power dissipation factor of ˜380 kW/g of Au. However, this capacitive heating approach carries a high risk of uncontrolled heat production in the body because of the finite electrical conductivities of the human tissues and their heterogeneities.